Cells may represent analytes of interest. Optical measuring methods (e.g., scattered light or fluorescence measurements) and magnetic detection methods (e.g., for detecting a cell type marked by magnetic labels) have been used for cell measurement and cell detection.
For magnet-based measurements, magnetically marked cells may be sorted from a complex cell suspension (e.g., a blood sample) by magnetophoresis. The magnetic marking is achieved by introducing cell-specific markers into the complex cell sample. Magnetophoresis has been used for sorting magnetically marked cells and magnetic particles.
Cell measurements in diagnostics and science involve measuring cell types (e.g., disseminated tumor cells) that are only present in a blood sample in very small concentrations. Thus, the loss of cells during sample preparation is undesirable. To quantify cell concentrations or to reliably detect specific cells, a prior enrichment of the cells to be determined from a suspension with a complex background is performed.
Enrichment of cells has been performed using centrifuging techniques, immunochromatography, and magnetic enrichment (MACS). In such methods, the enrichment takes place statically (e.g., the cells are enriched on a vessel wall or in a portion of a centrifuge tube). The enrichment factor observed using such methods may lie in a range of 101 to 104 and is not sufficiently high. For example, in the case of centrifuging techniques, mechanical loading of the cells may be unavoidable.
Conventional methods of magnetophoresis for dynamic cell enrichment tend to provide a low enrichment factor that does not exceed an enrichment of 100-fold. An example of magnetophoresis in a laminar flow is described by Jung et al. in Applied Physics Letters, 2008, 93, 223902.